It is generally characteristic of liquid crystalline systems that they contain a large amount of amphipatic molecules i.e. molecules (containing both hydrophobic and hydrophilic groups) beside the solvent. For example Moucharafieh and Frieberg ("First comparison between aqueous and nonaqueous lyotropic liquid crystals": Mol. Cryst. Liq. Cryst. 49 Letters 231-238, 1979) describe such regular systems wherein the amount of amphipatic material is 55% by weight if water is used as solvent and more than 45% by weight if ethylene glycol is the solvent (the balance is solvent).
Similar results were obtained in the course of our experiments. A large amount of surfactant material seems to be necessary independently on the ionogenic character of the amphipatic material. According to Tiddy et al. (J. Chem. Soc. Faraday Trans. I. 77 "Structure of liquid-crystalline phase formed by sodium dodecyl sulfate and water as determined by optical microscopy, X-ray diffraction and nuclear magnetic resonance spectroscopy") the sodium dodecyl sulfate (as a typical anionic surfactant material) forms a liquid crystalline system with water in a concentration of &gt;67% by weight.
In addition to the large amount of the surfactant material further problems arise in connection with the liquid crystalline systems. Heusch ("Flussig-kristalline Eigenschaften von Tensiden" Proc. VII. Intern. Congr. on Surfactants, Moscow, 1978. pp. 911-940) examined anionic, cationic and non-ionic surfactants and found that the viscosity (measured by Hoppler viscosimeter) of systems having lyotropic liquid crystalline structure exceeded the upper measuring limit of the viscosimeter (=50,000 mPa.s). A system having such high viscosity cannot be used in practice or one useful only in some extreme fields, e.g. as cleaning gel.
Considerable effort has been made to develop a liquid crystalline system having a surfactant content below the lower limit of the above mentioned concentration range of 45-70% by weight. The common feature of these compositions is that they contain another amphipatic material, called co-surfactant, capillaractive material or amphiphil, in addition to the surfactant. Danielson investigates ("The association of alkyl-chain salts in apolar media", Proc. VII. Intern. Congr. on Surfactants, Moscow, 1978. pp. 1010-1037), after Ekwall, systems containing sodium octanoate as surfactant material in an amount of 6-27% by weight, 5-33% by weight of water and decanol as co-surfactant in an amount of 70-95% by weight. Considering that the decanol serves as both between a the surfactant and co-surfactant material, the result obtained is not surprising. James and Heathcock arrive at the same conclusion ("Electron and optical microscopy study of the lamellar mesophase region of the water/sodium octanoate/decanol ternary system", J. Chem. Soc. Faraday Trans. I. 77, 2857-2865 1981).
The formation of a liquid crystalline structure is very advantageous as it assures the thermodynamic stability of a composition and the sedimentation stability of the material dispersed therein. The advantageous properties of the known liquid crystalline systems, however, cannot be utilized partly due to economic reasons (attributed to the high concentration of the surfactant and/or co-surfactant materials), partly due to the extremely high viscosity (several hundred thousand mPa.s) of these compositions.